The friend that gave me the rifle stated that it was 9x57R. I cast the chamber and found that it seemed to meet the dimension for 9x57R so I bought RCBS dies and formed brass from 8x57R brass which was available. I have fired it a few times with cast 9mm bullets with no problems. I haven't spent the time to come up with a load that regulates the barrels. Another factor was that I couldn't find a rimmed version of the MS 9x56mm, which was the only 56mm cartridge in "Cartridges of the World" Do you know of a 9x56R round?
Jim